Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1246 AM EDT Fri May 08 2020 Valid May 08/0000 UTC thru May 11/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Energy digging southeast from the northern Plains to the OH Valley and Mid-Atlantic... ...Strong vortex over southeast Canada and the Northeast... ...Deepening surface low from the OH Valley to the Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 08/00Z GFS and the 07/12 ECMWF and 12Z GEFS Confidence: Below average During the day today, Friday, shortwave energy will be crossing the OH Valley and will be attempting to phase with very strong northern stream height falls/troughing associated with a vortex settling south over eastern Ontario and southwest Quebec. This will lead to strengthening low pressure up across the OH Valley along a frontal boundary, and this low center will then cross the Mid-Atlantic by this evening. On Saturday, the coupling/phased resultant of energy moving into the Northeast will yield a highly anomalous closed low and associated upper trough over the Northeast U.S. (500 mb heights 3 to 4 standard deviations below normal), with likelihood of a rapidly deepening surface low lifting up across or just offshore of coastal New England. The model spread with the low track itself across the OH Valley and Mid-Atlantic is rather small, however the 08/00Z GFS was a bit of a strong outlier with its intensity compared to the remaining guidance despite the fact that the 00Z run of the GFS tempered the depth of the low a bit compared with previous runs. The model spread worsens with respect to New England as the low tracks northeastward and deepens with time. The 08/00Z NAM was still ends up flatter/weaker and on the east side of the model spread, and has agreement from the 07/12Z UKMET. So, the GFS and ECMWF are still suggestive of stronger/quicker phasing relative to the NAM/UKMET/CMC camp which allows the low center to tuck in closer to the New England coast before exiting up across southeast Canada. The latest available ensemble means do not exactly foster high confidence in this forecast. Based on the latest trends, ensemble means and clustering, a blend of the 08/00Z GFS and 07/12Z ECMWF and their respecting means remain preferred for the system because that blend tempers the stronger GFS over the OH Valley and Mid-Atlantic while also promoting at least a modest eastward shift in the low track relative to New England. Given the run to run variability and model spread, confidence is below average. ...Shortwaves/surface low impacting the northern Plains and Midwest this weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 08/00Z GFS, 07/12Z CMC and ECMWF Confidence: Average Downstream of a sharp and elongated mid-level ridge in place over western North America today through Saturday, and embedded within deep layer north-northwest flow over central Canada, a pair of shortwaves will drop down out of Canada and down across portions of the northern Plains and Midwest this weekend. The lead shortwave will have a low center and cold front associated with it which will cross the Dakotas on Saturday and then gradually weaken as it crosses the Midwest on Sunday. Model spread is relatively minimal, but the 08/00Z GFS tended to be stronger and faster than other global guidance and the latest NAM. Of the global models, the 07/12Z UKMET remained the most questionable at this time as it has a slower shortwave evolution and surface reflection relative to the model consensus and the ensemble means. ...Shortwave energy crossing southern CA by Sun morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show a weak shortwave crossing areas of coastal southern CA and then the Desert Southwest on Sunday. Given the modest spread in timing and depth relating to this energy, a general model blend remains the preferred option. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Bann